1. Field of the Invention
This invention relates to underdrain blocks used in draining and backwashing filtering media in a filter bed, generally referred to as a gravity filter, where liquid is supplied to the filtering media from a position vertically above the media and passes down through the media to an underdrain system comprising a plurality of said underdrain blocks and a method of installing an underdrain block lateral comprising at least one underdrain block.
2. Description of Related Art
Filter beds where liquid is supplied to the filtering media from a position vertically above the media and passes down through the media, commonly referred to as gravity filters, often use underdrain blocks to form the drainage and backwash system in the bottom of the filter. The filtering media sits atop these underdrain blocks. The solution to be filtered is introduced into the top of the filter and gravity causes it to pass vertically downward through the filtering media and into the underdrain blocks. The underdrain blocks channel the filtered fluid which has passed through the filter media away from the filter.
In addition, it is occasionally necessary to clean the filter media. This is accomplished through a backwash procedure in which water and/or air is forced through the underdrain blocks and upward through the filter media against the force of gravity.
There are a variety of underdrain blocks known in the art, for example, U.S. Pat. No. 2,929,505 to Wanner, U.S. Pat. No. 5,108,627 to Berkebile et al., U.S. Pat. Nos. 6,991,726 and 7,192,521 to St. Germain. U.S. Pat. No. 5,108,627 describes a common underdrain block and is incorporated herein by reference.
Underdrain blocks are generally square or rectangular in cross section and have a long longitudinal axis as compared to their cross section. The underdrain blocks are approximately 4 feet in length. They are attached end-to-end using a snap-fit bell and spigot arrangement to form long sections of up to 96 feet called laterals. The laterals are installed side-by-side in the bottom of the filter to form the underdrain system. Each lateral is placed between a set of anchor rods and is in close proximity to one another. Often, the laterals will be placed in a layer of concrete to secure them in position and level the assembly.
The laterals are heavy and can be awkward to handle due to their length. In addition, they must be carefully placed between the anchor rods with as little as 1.5 inches between the sidewalls of adjacent laterals. The laterals can weigh hundreds of pounds, depending on length and whether media retainer is installed. Therefore, it takes several workers to position and install an underdrain block in the bottom of a filter and, often, due to the awkward way in which the laterals must be handled, the installation workers receive bruises and scrapes during the installation.
While underdrain blocks, such as the one described in U.S. Pat. No. 5,108,627, may include flange members on the sides to assist in handling and placement of the underdrain blocks, due to the close proximity in which the underdrain blocks must be placed, the flanges cannot extend very far from the side of the underdrain block and are not very useful when trying to position one lateral in close proximity with another. Alternatively, ropes have been used to lower the laterals into position, but this becomes very messy when the underdrain blocks are being set in wet concrete.
Thus, current underdrain blocks tend to be unwieldy to handle and difficult to position when they have been formed into laterals for potentially resulting in injury to the workers installing the laterals, and loss of productivity.